1. Field of the Invention
The present disclosure relates to a manufacturing method of a non-volatile memory element, the non-volatile memory element, and a non-volatile memory device. More particularly, the present disclosure relates to a manufacturing method of a variable resistance non-volatile memory element, the variable resistance non-volatile memory element, and a variable resistance non-volatile memory device.
2. Description of the Related Art
In recent years, with progresses of digital technologies, electronic devices such as portable information devices and information home electric appliances have been developed to provide higher functionalities. For this reason, there have been increasing demands for an increase in a capacity of a variable resistance element, reduction in write electric power in the variable resistance element, reduction in write/read time in the variable resistance element, and a longer life of the variable resistance element.
Under the circumstances in which there are such demands, it is said that there is a limitation of miniaturization of the existing flash memory using a floating gate. In contrast, it is expected that a variable resistance element (variable resistance memory) including a variable resistance layer as a material of a memory section can achieve further miniaturization, a higher speed, and lower electric power consumption, because it can be implemented by a memory element having a simple structure including a variable resistance element.
In a case where the variable resistance material is used as the memory section, its resistance value is changed from a value corresponding to a high-resistance state to a value corresponding to a low-resistance state or from the value corresponding to the low-resistance state to the value corresponding to the high-resistance state, by, for example, application of an electric pulse. In this case, it is necessary to clearly distinguish the value corresponding to the low-resistance state and the value corresponding to the high-resistance state from each other, stably change the memory section between the low-resistance state and the high-resistance state at a high speed, and retain these two values in a non-volatile manner. So far, various proposals have been made to stabilize such a memory characteristic and miniaturize the memory element.
As one of such proposals, International Publication No. 2008/149484 discloses a non-volatile memory element which includes two electrodes (upper electrode, lower electrode), and a variable resistance layer sandwiched between these electrodes, the variable resistance layer having a stacked-layer structure including a first tantalum oxide layer which is lower in oxygen content atomic percentage and a second tantalum oxide layer which is higher in oxygen content atomic percentage. The first tantalum oxide layer is disposed on and above the lower electrode. The second tantalum oxide layer is disposed between the first tantalum oxide layer and the upper electrode. When an electric pulse having a positive voltage on the basis of the lower electrode is applied to the upper electrode in this non-volatile memory element, oxygen atoms migrate from the first tantalum oxide layer to an interface between the second tantalum oxide layer and the upper electrode, which allows the variable resistance layer to be easily changed to the high-resistance state. On the other hand, when an electric pulse having a negative voltage on the basis of the lower electrode is applied to the upper electrode in this non-volatile memory element, oxygen atoms staying at the interface between the second tantalum oxide layer and the upper electrode migrate to the first tantalum oxide layer, which allows the variable resistance layer to be easily changed to the low-resistance state.